Internal shoe drum brakes



Jan. 3, 1967 K. J. WVELLS 3,295,637

INTERNAL SHOE DRUM BRAKES Filed April 16, 1965 2 Sheets-Sheet l Jan. 3, 1967 K. JtwELLs 3,295,637

INTERNAL SHOE DRUM BRAKES Filed April 16, 1965 2 Sheets-Sheet 2 United States Patent Ofitice 3,295fi3? Patented Jan. 3, 1967 3,295,637 INTERNAL SHOE DRUM BRAKES Kenneth John Wells, Sutton Coidfield, England, assignor to Girling Limited, Birmingham, England, a British company Filed Apr. 16, 1965, fier. No. 448,625 4 Claims. (Cl. 18878) This invention relates to improvements in internal shoe drum brakes of the kind in which a shoe is applied to a rotatable drum by a piston working in an hydraulic cylinder to which fluid under pressure is supplied from a master cylinder, or the like.

When the brake is applied the shoe moves outwardly into engagement with the drum and the end of the shoe which is engaged by the piston is frequently required to scrub across the outer end of the piston, and it is believed that this may be a cause of brake squeal. Attempts have been made to overcome this scrubbing by the provision of a roller between the end of the shoe and the piston.

According to my invention, in a brake of the kind set forth there is interposed between the piston and the end of the shoe an intermediate member or insert which is in rocking engagement with the piston so that its outer end can move with the end of the shoe in the application of the brake.

A preferred construction is illustrated by way of example in the accompanying drawings in which:

FIGURE 1 is an end elevation of a brake embodying my invention;

FIGURE 2 is a side elevation of the intermediate member or insert by itself;

FIGURE 3 is an end view of a divided spring ring for retaining the intermediate member or insert in the piston;

FIGURE 4 is a section of the piston with the intermediate member or insert in position; and

FIGURE 5 is a plan of a modified intermediate member or insert incorporating means for locating the shoe against axial movement.

In the brake shown in FIGURE 1, 1t and 11 are opposed arcuate brake shoes mounted on a stationary backplate 12 and carrying friction linings 13 for engagement with a rotatable drum (not shown). The shoe is adapted to be moved outwardly into engagement with the drum by a piston 14 working in an hydraulic cylinder 15 mounted on the back-plate. The closed end of the cylinder provides a torque-taking abutment with which the web of the shoe 11 is in sliding and rocking engagement. The shoe 11 is applied to the drum by a piston Working in another hydraulic cylinder (not shown) mounted on the back-plate in a position diametrically opposite the cylinder 15 and providing a torque-taking abutment for the shoe 10.

In the usual brake of this kind the piston 14 engages directly with the end of the web of the shoe 10. According to my invention there is provided between the piston and the shoe web an intermediate member which is in rocking engagement with the piston and which is shown in detail in FIGURES 2, 3 and 4. The intermediate member is of circular cross-section and comprises a head 16 and a shank or stem 17. The outer end of the head is flat or substantially fiat for engagement with the radiused end of the shoe Web and its peripheral edge is charnfered as shown at 18. At the inner end of the head there is an annular partspherical surface 19 adapted to co-operate with a complementary annular surface on the outer end of the piston. The stem 17 is received in an axial recess 21 in the piston extending in from its outer end. The diameter of the stem is less than that of the recess to permit the required rocking movement of the member relative to the piston, and it is frictionally retained in the recess by a split spring ring 22 mounted in an annular groove in the stem and frictionally engaging the wall of the recess. The inner end of the stem is preferably chamfered or tapered as shown at 23.

The engagement of the stem 17 in the recess 21 prevents excessive angular movement of the intermediate member relative to the piston which could be caused by additional movement of the shoe when the lining is worn.

If desired, the outer face of the head 16 of the intermediate member may be formed with spaced lugs 24 between which the end of the shoe web is received to locate the shoe against movement in the direction of the axis of the brake as shown in FIGURE 5.

Preferably the outer end of the hydraulic cylinder is sealed by a rubber or other boot 25 which fits over the open end of the cylinder and has an inner annular flange 26 with an enlarged extremity fitting around the intermediate member between the head 16 and the end of the piston as shown at FIGURE 1.

The outer end of the boot has a slot for the passage of the reduced end of the shoe web which is a close fit in the slot.

The assembly is thus effectively sealed against the entry of water or dirt.

The construction described above has been found to be more effective than a roller in preventing squeal, and as the intermediate member is in rocking engagement with the piston any offset or cross-binding forces on the piston caused by movement of the shoe end in a direction at right angles to the axis of the piston are eliminated or reduced.

I claim:

1. A shoe drum brake comprising a stationary backplate, a shoe mounted on the back-plate for engagement with a rotatable drum, an hydraulic cylinder mounted on the back-plate, a piston movable in the cylinder for applying the shoe to the drum, an intermediate member located between the piston and the shoe and in rocking engagement with the shoe, a stem on said intermediate member adapted to enter an axial recess in the piston of greater diameter than the stem to provide a loose fit therebetween, a forward face on said intermediate member for engagement with the shoe, and an annular part spherical rear face on said intermediate member co-operating with a complementary part-spherical surface on the piston being located immediately forward of said axial recess.

2. A shoe drum brake as claimed in claim 1, wherein a spring ring located in an annular groove in said stem has a yieldable engagement with the axial recess in which the stem is received to permit rocking movement of said intermediate member relative to said piston.

3. A shoe drum brake as in claim 1 wherein the intermediate member has spaced lugs between which the end of the shoe is received.

4. A shoe drum brake as in claim 1 including a rubber boot which seals the end of the hydraulic cylinder and the engagement between the intermediate member and the piston.

References Cited by the Examiner UNITED STATES PATENTS 2,041,463 5/1936 Frank 188-152 2,583,888 1/1952 Schnell 188-452 2,836,961 6/1958 Brand 188152 2,906,517 9/1959 Goepfrich 188-152 MILTON BUCHLER, Primary Examiner.

B. S. MOWRY, Assistant Examiner. 

1. A SHOE DRUM BRAKE COMPRISING A STATIONARY BACKPLATE, A SHOE MOUNTED ON THE BACK-PLATE FOR ENGAGEMENT WITH A ROTATABLE DRUM, AN HYDRAULIC CYLINDER MOUNTED ON THE BACK-PLATE, A PISTON MOVABLE IN THE CYLINDER FOR APPLYING THE SHOE TO THE DRUM, AN INTERMEDIATE MEMBER LOCATED BETWEEN THE PISTON AND THE SHOE AND IN ROCKING ENGAGEMENT WITH THE SHOE, A STEM ON SAID INTERMEDIATE MEMBER ADAPTED TO ENTER AN AXIAL RECESS IN THE PISTON OF GREATER DIAMETER THAN THE STEM TO PROVIDE A LOOSE FIT THEREBETWEEN, A FORWARD FACE ON SAID INTERMEDIATE MEMBER FOR ENGAGEMENT WITH THE SHOE, AND AN ANNULAR PART SPHERICAL REAR FACE ON SAID INTERMEDIATE MEMBER CO-OPERATING WITH A COMPLEMENTARY PART-SPHERICAL SURFACE ON THE PISTON BEING LOCATED IMMEDIATELY FORWARD OF SAID AXIAL RECESS. 